Details

Our Meditation Benches are made from beautifully finished birch plywood and feature folding legs for ease of storage and portability. The one-inch foam cushion that tops our bench is covered with durable cotton fabric that can be removed for laundering. A drawstring carrying bag with handle is included.

I got this bench years ago when it was less expensive. It was the only option that worked for me since I can't sit cross legged for more than a few minutes b/c of back, knees, ankle injuries, and tight hips.
I use it on top of a Mexican yoga blanket w/a fleece one on top and I'm careful to place it properly before I sit, so the legs have never collapsed on me for as long as I have been using it.
Adding a locking feature would probably bring the cost up, and the legs are made to collapse for ease of portability (hence the carrying bag.)
It's a great bench, and despite my back issues I am able to sit on it for an hour (after a few weeks of practice) and my back does not scream at me. I'd definitely recommend it, especially since the benefits of gaining a stronger back could eliminate the cost of massage or chiropractic, giving you repeated returns on your investment.
Don't let the price or lack of locking legs deter you if you're serious about finding a comfortable sitting item for a dedicated meditation practice. It's worth a try, and finding the most comfortable way to sit is one of the keys to developing your practice.

Because of instability, and tendency for legs to collapse with even slight shifts, I would not recommend this until a latching or locking mechanism was put in place. Since I can't use it I am unable to tell how comfortable the position would be over time.